This invention relates to a control mechanism for a fuel supply member of an internal combustion engine.
Automatic speed change gears have been proposed in which a fuel supply device and conventional, manually operated, synchronously meshed transmission gears are automatically controlled, together with a clutch mechanism. The automatic speed change gears are arranged such that the clutch mechanism is engaged or disengaged in response to a predetermined number of steps of a stepping motor. Controlled in a one-to-one relationship by the stepping motor is either a control rod of a fuel injection pump or a drive lever of a throttle valve of a carburetor. The stepping motor controls fuel supply during starting, changing of speed and stopping of the vehicle. In order to minimize shock when the clutch mechanism is disengaged during gear changes, the stepping motor is gradually stepped a predetermined number of steps "s" in a reverse direction to reduce torque of the driving system. The number "s" is based on the relationship between engine r.p.m. and the number of steps and is provided from the memory of a control computer. When "s" steps are completed, the clutch mechanism is disengaged. Conversely, when the clutch mechanism is being engaged, the stepping motor is stepped in the forward direction so as to provide sufficient driving torque which matches the engaging degree of the clutch mechanism and thereby minimizing the time for speed change. An example of automatic speed change gears of this type are described in U.S. Pat. No. 4,194,608.
A problem in the above described system is that the described driving torque is not always produced by a predetermined number of steps by the stepping motor. Because of play in the fuel injection pumps of present-day diesel engines, the relationship between the number of stepping motor steps and the driving torque are not always constant. Therefore, for example, when the clutch mechanism is engaged after gear changes, the force of the engine brake is exerted in some vehicles. Conversely, the engine is undesirably reved up in other vehicles. This lack of constancy is produced also in systems controlling the throttle valve of a carburetor, though to a lesser degree.
The above noted problem will be described further in connection with FIG. 1 which shows a conventional fuel control member in an internal combustion engine. A drive lever 5 for either a fuel control rod of a fuel injection pump or a throttle valve of a carburetor is supported from a base frame 6 by a shaft 9. Controlling movement of the lever 5 is a link 3 coupled to a stepping motor (not shown). An initial position of the drive lever 5 is adjusted by a set screw 8 supported by the base frame 6. The set screw 8 is set by a lock nut 7 at a position that provides a suitable idle r.p.m. of the engine. For example, with the position of drive lever 5 shown by dotted lines, an idle r.p.m. of 250 is produced.
Because of the above noted problems, the characteristic of engine r.p.m. (in this case the load is supposed to be constant) in relation to the operating angle ".alpha." of the drive lever 5 will vary for different vehicles as shown by the curves 41 and 42 in FIG. 2. The solid curve 42 represents the desired characteristic while the dotted curve 41 represents an undesirable shifted characteristic. If, as shown by the curve 41, a desired shifting r.p.m. of, for example 1500 is reached prematurely, the engine r.p.m. becomes abnormally high when the clutch mechanism is engaged or disengaged while changing gears. Thus, speed change control is not smooth because a matching between the output and the load torques is not provided.
To provide the desired shifting r.p.m. of 1500, the characteristic represented by the dotted curve 41 in FIG. 1 can be shifted. This is done by adjusting the set screw 8 so that the drive lever 5 will produce the desired engine r.p.m. after movement over the operating angle ".alpha." provided by the given number of steps "s" given to the stepping motor. However, in this case, as shown in FIG. 3, the idle r.p.m. is undesirably deviated or changed.
The object of the present invention, therefore, is to provide for an internal combustion engine a fuel control mechanism that establishes consistent engine r.p.m. for automatic gear shifting.